Project 3: The Role of ApoE in Neuroplasticity and A Clearance using iPS Cell-Derived Astrocytes Project Summary/Abstract This proposal aims to utilize patient iPS cell-derived astrocytes to investigate the role of apolipoprotein E (apoE) on AD risk at the molecular level. While mouse models have greatly improved our understanding of AD pathogenesis, the molecular and cellular mechanisms by which apoE influences human neuronal function and degeneration remain largely unknown. ADRC patient-derived astrocyte will be used to determine how APOE genotype affects astrocyte function and using a novel human astrocyte/neuronal co-culture, determine the role of apoE isoforms on synapse formation/plasticity and to investigate how synaptic vulnerability to A and tau is influenced. Recent studies suggest that apoE may also influence astrocyte-mediated A clearance. We will therefore determine whether the different apoE isoforms alter the rate of A phagocytosis by human astrocytes and influence the neuron-neuron transmission of tau. The proposed studies will utilize 12 lines of patient- derived iPS cells provided by the ADRC iPS Cell Core (6-APOE 3/3 and 6-APOE 4/4). In collaboration with the iPS Cell Core, we will also use CRISPR-mediated genome editing to convert an APOE 4/4 iPS cell line into an isogenic APOE 3/3 line to allow us to compare genetically homogenous human astrocytes that differs only by the APOE allele. Lastly, iPS cell-derived astrocytes will be transplanted into xenotransplantation- compatible Rag-5xfAD and Rag-tau mice to examine the effects of apoE on amyloid and tau pathology in vivo.